This invention relates generally to building construction and more particularly to the fabrication of concrete wall panels that are tilted up into place and attached to form the walls of a building.
Tilt-up concrete wall panel construction has been used for years to construct commercial buildings such as warehouses, factories, and the like. In general, such construction entails building a rectangular concrete form, usually on site, placing steel reinforcing bars (rebar) or other reinforcement in the form, filling the form with concrete, and, after the concrete cures, tilting the resulting concrete panel into place to form a wall section. Numerous wall sections generally are fabricated and attached together and to framing members of the building to form complete walls. Utility conduits may be embedded within the wall sections as needed to provide for electricity and plumbing. U.S. Pat. No. U.S. Pat. No. 3,394,523 of Sackett, U.S. Pat. No. 4,104,356 of Deutsch et al., U.S. Pat. No. 3,604,174 of Nelson, and U.S. Pat. No. 4,856,244 of Clapp disclose various examples of tilt-up concrete wall panel construction techniques.
While traditional concrete wall panel construction techniques have been somewhat successful in constructing commercial buildings, they nevertheless have been fraught with a variety of inherent problems and shortcomings. Among these are the fact that, in most cases, the forms into which the concrete is poured usually are fabricated from wood or metal on site at a worksite such as, for example, on the ground adjacent to where they are to be tilted up to form a wall. The on-site building of such forms is a tedious and time consuming process and further requires a high level of skill on behalf of workers to assure that the panels are all the correct size and configuration. In addition, where wooden forms are used, the process of disassembling the framing members and discarding them after the concrete cures can be time consuming and wasteful. In most cases, reinforcing stakes, spacers, or blocks must be used to reinforce the sides of the concrete forms so that they do not bow outwardly or otherwise deform under the substantial pressures created by the wet concrete poured into the forms. Installing these reinforcing members is yet another time consuming step in the process.
Another problem with prior art techniques relates to the installation within the concrete forms of the rebar, wire mesh, or other reinforcing members that are to be embedded within the finished wall sections. More particularly, the construction of a matrix of reinforcing members is a time consuming and tedious process. This is particularly true in systems where the walls of the form are made from inwardly open channel shaped steel or formed sheet metal. The reason is that the reinforcing members must be installed in the mid-portion of the form between the inwardly projecting lips of the walls. In order the accomplish this, the framing members must be cut to be longer than the distance between the facing edges of opposed lips and jockeyed into place in the middle of the form before being secured in place within the form.
There exists a need for an improved tilt-up concrete wall form and a method of fabricating concrete wall sections using the form that addresses and solves the above mentioned and other problems of the prior art. The form should be lightweight, strong, and portable so that they can be manufactured to exacting tolerances at a remote location and delivered to a job site on a truck for immediate use. Further, the form should be usable without the need for any on-site form construction and without the need to reinforce the walls of the form against bowing under pressure when concrete is poured into the form. No deconstruction of the form should be required after the concrete cures and no waste that requires disposal should be generated during use of the form. At a remote form fabrication facility, fabrication should be quick and efficient and the installation of a matrix of reinforcing rebar in the mid-portion of the form should be accurate, quick, and efficient. An improved method of fabricating tilt-up concrete wall sections using such an enhanced form also should be included. It is to the provision of such a form and method of construction that the present invention is primarily directed.
Briefly described, the present invention, in a preferred embodiment thereof, comprises an improved form for fabricating tilt-up concrete wall sections and an improved method of fabricating tilt-up concrete wall sections using the form. The form has generally C-shaped or channel-shaped roll formed sheet metal frame members that are welded together at their ends to define the shape of the form, which may be rectangular for many applications but that also may take on other shapes according to application specific requirements. A matrix or mat of crisscrossed rebar is disposed in the form to provide reinforcement when concrete is poured into the form during fabrication of a concrete wall section. Each rebar of the matrix extends between opposed frame members of the form and is cut to be short enough to slip into the mid-portion of the form past the inwardly extending flanges of the C-shaped frame members. A unique bracket is slidably disposed on the ends of at least some of the rebars of the rebar mat and each bracket is spot welded to the corresponding frame member and to its rebar. This configuration establishes structural integrity of the assembly. Brackets may be disposed on the ends of each rebar or just on the ends of selected ones of the rebars as necessary to hold the reinforcing mat in place and to establish the desired structural integrity. The form is fabricated at a remote manufacturing facility as follows. First, the roll formed sheet metal frame members are cut to size and welded together at their ends to define a frame of the appropriate size and shape. The generally channel-shaped frame members are oriented with their open or channeled sides facing inwardly toward the middle of the form. In other words, the flanges on the edges of the frame members face inwardly toward each other and thus may be referred to as inwardly extending flanges. Down turned lips preferably are formed along the edges of the flanges to add strength and rigidity.
The crisscrossed rebar mat is then constructed by arranging individual rebars and welding them together at their intersections. A bracket is slid onto the ends of each rebar until the rebar ends protrude from the base of the bracket. With the mat constructed and brackets installed, the entire rebar mat can be positioned in the form. Since the rebars are cut short as mentioned above, the entire rebar mat slips easily past the inwardly extending flanges of the frame members and into the middle of the form. With the rebar mat properly positioned within the form, the brackets on the ends of the rebars are slid toward the frame members until the base of each bracket rests against the outside panel of the frame member between its inwardly projecting flanges. The base portions of the brackets are configured to extend between the flanges of the frame members, thereby automatically centering the rebar mat in the middle of the form. The bases of the brackets are then spot welded to the frame members and the end of each rebar is spot welded to its respective bracket to complete the form. It will thus be seen that the rebar mat is automatically centered and held in place by the brackets. Further, since the rebar mat is welded together and to the brackets, and the brackets are welded to the frame members, the completed form is strong and rigid and maintained in its proper shape by the installed rebar mat.
Since the forms of the present invention are lightweight and rigid, they may be handled, shipped to a jobsite where they are to be used to fabricate concrete wall sections, and unloaded at the job site without fear of the forms becoming warped or deformed. Once at the jobsite, the forms are laid flat on a casting surface, such as a concrete slab, preferably near the location where concrete wall sections are to be erected. The forms are then filled with concrete from a concrete truck, a pump truck, or other source. Again, since the brackets are welded to the frame members and the rebars of the mat welded to the brackets, the rebar mat ties the framing members together and prevents them from bowing or bulging outwardly under the pressure of the wet concrete. Accordingly, no further reinforcing blocks or other reinforcement is required prior to pouring the concrete into the forms as is common in prior art systems.
When the concrete is-cured, the resulting concrete wall sections may be tilted up using a derrick or crane and sling arrangement until they are in their proper positions, whereupon they may be attached together and/or to structural support members of the building to form walls. All of the elements of the form remain with the finished concrete wall sections and become a part of the finished wall. Accordingly, no disassembly of the form is required after the concrete cures and no waste that must be discarded is produced.